Did they compare their Teflon findings to those of rain on bare metal surfaces? Or the configuration of those surfaces at microscopic levels?
It sounds like they are creating miniature capacitors by placing a charge (raindrop) on an insulator, seperating them a short distance from a grounded surface. In such cases, the electrical potential gradient can reach very high levels even for small charges. When those potentials reach sufficient levels, they can break chemical bonds and break down the insulating properties of coatings. Sometimes the trick is to make the coatings "semiconductive". Not perfect insulators, but with a high resistance that allows surface charges to bleed off.